It doesn't sound like you were taking it correctly. You should be taking the "active" pills for 3 weeks and the "inactive" pills for 1 week, during which time you will have a period. Actually yasmin is one of the best pills you can take, it's the most used pill in america.
You may also be experiencing some irregularities because you just had a baby. It will take 4-6 months of using the pill to get your cycle back on a regular pattern. I wouldn't give up on yasmin just yet. Also, you should probably be using a back-up method of birth control so you don't get pregnany again.